The invention relates to a method for increasing the utilization of the braking torque of a retarder in a motor vehicle. The invention further relates to conducting away heat generated in the retarder during the braking operation using a coolant. The invention also relates to operating secondary loads in a cooling system even if not required.
In order to cool vehicle components, for example hydrodynamic brakes, internal combustion engines, etc., use is generally made today of coolant circuits comprising a coolant, preferably water with appropriate antifreeze additives. In such circuits, a specific quantity of coolant per time unit flows through the component to be cooled. The coolant absorbs heat that is to be conducted away from the component and conveys the heat to a radiator, for example a ribbed radiator, or to a heat exchanger. The radiator or exchanger outputs the absorbed and conveyed quantity of heat into the environment or to another coolant circuit. The cooling power of such a system is determined essentially by the efficiency of the individual system components, for example the delivery capacity of the coolant pump.
In order to protect the engine cooling system against overheating when a retarder is switched on, it has therefore been proposed in
to reduce the retarder braking power as a function of the engine speed, and thus the speed of the coolant pump.
A disadvantage with this method or this control system is that the retarder braking torque is reduced very early, and as a result the braking power of the retarder is utilized only insufficiently.
The object of the present invention is therefore to specify a method and a device for carrying out the method with which the disadvantages of the prior art are avoided and the retarder braking torque can be utilized better than hitherto, that is to say the retarder availability is increased.
This object is achieved according to the invention in that at least one secondary load and/or at least one of the following devices of the cooling system in the vehicle:
a switched fan
a switched thermostat
a coolant pump
a bypass valve in the cooling circuit
is actuated as a function of the instantaneous or future braking requirement.
It is particularly advantageous if at least the following retarder operating states:
switching on the retarder
requested or actually selected braking level of the retarder
are distinguished. In terms of actuation, the following variants are conceivable:
everything depends on the engine control system. It controls the engine, the fan and the retarder; or
each of the aforesaid assemblies has its own control system and these communicate with one another; or
retarder and fan have a common control system.
A particularly interesting variant consists in not sensing the instantaneous braking requirement or not exclusively sensing the instantaneous braking requirement, but also the future braking requirement in terms of predictive driving. The future braking requirement can be defined here by means of a navigation system in which the route ahead is examined by means of, for example, a satellite system (so-called global positioning system).
According to the invention, the retarder availability with respect to the maximum possible level of braking torque can be increased by virtue of the fact that a switched fan, for example that of the vehicle radiator, is connected into the circuit by the retarder electronics when the retarder switch-on instruction is present, as a result of which the efficiency of the cooling system is increased.
In order to avoid fuel being used unnecessarily by the fan which is connected into the circuit when the retarder is switched off, there is provision that when the retarder is OFF instruction is present, the fan is enabled again or switched off. Actuation takes place then only by means of the sensors of the engine cooling system. As an alternative to switching off or enabling the fan when the retarder is switched off, there may also be provision to switch off or enable the fan when the retarder braking torque drops below a specific value that is predefined at a low level.
In addition to a pure on/off logic system as described above, it is advantageously provided that in the case of multi-step fans or infinitely adjustable fans the actuation of the fan is carried out as a function of the requested retarder braking power, for example the selected retarder braking level. In principle, the fan according to the invention operates with a high rotational speed at high retarder braking levels, whereas at low retarder braking levels the fan is either entirely enabled or runs with only a reduced rotational speed.
In a further, developed embodiment of the invention, there may be provision for the thermostat which is preferably embodied as a 2/3-way valve in, for example, the coolant circuit of the vehicle cooling system to be switched as a function of retarder operating states.
There may be provision that if the cooling system is running in the bypass mode, i.e. the coolant fluid is being conducted past the vehicle radiator, the 2/3-way valve is actuated, after the retarder is switched on, in such a way that coolant fluid flows through the vehicle radiator in order to increase the cooling power of the cooling system.
The retarder availability can be increased further if not only the fan and the bypass valve are actuated as a function of the braking requirement but also a coolant pump, if said pump is one whose rotational speed can be actuated or regulated. In such embodiments there may be provision that the rotational speed of the coolant pump is increased when the retarder is switched on and decreased to the normal level when the retarder is switched off. With a coolant pump whose rotational speed can be adjusted, it is also possible to select the rotational speed as a function of the selected retarder braking level.
So that the heat generated by the retarder can be conducted away better than hitherto and not exclusively by means of the cooling system and from there into the environment, there is provision that secondary loads in the vehicle which do not have to be permanently in use are switched on if the retarder is switched on, in order to convert the braking work into useful work, with the result that the energy can be utilized more appropriately.
If the retarder is a secondary retarder, and there is no need whatsoever to restrict the invention to this, a separate heat exchanger is generally assigned to said secondary retarder. If the heat exchanger circuit has, like the engine cooling system, a bypass, in a particular refinement of the invention it is possible to operate the bypass similarly to the operation of the radiator bypass valve. The heat exchanger bypass in this instance is connected in a way analogous to the radiator bypass valve. That is, coolant is conducted through the heat exchanger when relevant for the braking mode of the retarder, and past the heat exchanger when the retarder is switched off.
In addition to the method described above, the invention also makes available a control device for carrying out the method. According to the invention there is provided a control or regulating system that comprises means, for example sensors, for sensing the retarder operating states or the instantaneous or future braking state. The system further comprises a control/regulating device that actuates vehicle assemblies such as secondary assemblies and/or devices of the cooling system as a function of the retarder braking states detected.